Caliburn Micro: как перемещаться в Windows phone silverlight

Я пытаюсь использовать Caliburn Micro в своем проекте Windows Phone 7. Но я получил исключение nullreferenceException при навигации по странице.

namespace Caliburn.Micro.HelloWP7 {
    public class MainPageViewModel {
        readonly INavigationService navigationService;

        public MainPageViewModel(INavigationService navigationService) {
            this.navigationService = navigationService;
        }

        public void GotoPageTwo() {
            /*navigationService.UriFor<PivotPageViewModel>()
                .WithParam(x => x.NumberOfTabs, 5)
                .Navigate();*/
            navigationService.UriFor<Page1ViewModel>().Navigate();
        }
    }
}

namespace Caliburn.Micro.HelloWP7
{
    public class Page1ViewModel
    {
         readonly INavigationService navigationService;

         public Page1ViewModel(INavigationService navigationService)
         {
            this.navigationService = navigationService;
        }
    }
}

может ли кто-нибудь сказать мне, в чем проблема моего кода? заранее спасибо.

вот загрузчик:

public class ScheduleBootstrapper : PhoneBootstrapper
{
    PhoneContainer container;

    protected override void Configure()
    {
        container = new PhoneContainer(RootFrame);

        container.RegisterPhoneServices();
        container.PerRequest<MainPageViewModel>();
        container.PerRequest<MainContentViewModel>();
        container.PerRequest<Page1ViewModel>();
        AddCustomConventions();
    }

    static void AddCustomConventions()
    {
        ConventionManager.AddElementConvention<Pivot>(Pivot.ItemsSourceProperty, "SelectedItem", "SelectionChanged").ApplyBinding =
            (viewModelType, path, property, element, convention) =>
            {
                if (ConventionManager
                    .GetElementConvention(typeof(ItemsControl))
                    .ApplyBinding(viewModelType, path, property, element, convention))
                {
                    ConventionManager
                        .ConfigureSelectedItem(element, Pivot.SelectedItemProperty, viewModelType, path);
                    ConventionManager
                        .ApplyHeaderTemplate(element, Pivot.HeaderTemplateProperty, viewModelType);
                    return true;
                }

                return false;
            };

        ConventionManager.AddElementConvention<Panorama>(Panorama.ItemsSourceProperty, "SelectedItem", "SelectionChanged").ApplyBinding =
            (viewModelType, path, property, element, convention) =>
            {
                if (ConventionManager
                    .GetElementConvention(typeof(ItemsControl))
                    .ApplyBinding(viewModelType, path, property, element, convention))
                {
                    ConventionManager
                        .ConfigureSelectedItem(element, Panorama.SelectedItemProperty, viewModelType, path);
                    ConventionManager
                        .ApplyHeaderTemplate(element, Panorama.HeaderTemplateProperty, viewModelType);
                    return true;
                }

                return false;
            };
    }

    protected override object GetInstance(Type service, string key)
    {
        return container.GetInstance(service, key);
    }

    protected override IEnumerable<object> GetAllInstances(Type service)
    {
        return container.GetAllInstances(service);
    }

    protected override void BuildUp(object instance)
    {
        container.BuildUp(instance);
    }
}